Holographic imaging is well known for retrieving both the amplitude and phase information of the object. Ironically, although the use of coherent illumination led to the realization of viable holographic imaging, it also restricted the wide usage of the holographic imaging. The possibility of incoherent holography has been studied but it was not able to achieve the acceptable quality of hologram until recently. Through the development of digital electronic devices and computer science in the recent decade, many interesting techniques have been proposed to acquire holographic information under the incoherent illumination. One approach that uses the self-interference shows promise for practical applications. This approach separates the light from an object into two paths and causes beams from the same object point to interfere with each other. Unfortunately, the spatial incoherence of the light from the object washes out the fringe of the recorded intensity image. Because of this, the complex hologram must be computationally retrieved from multiple phase-shifted images.
Recently, the inventor reported successful achievement of holographic recording and reconstruction of a natural outdoor scene with a holographic camera based on the self-interference incoherent digital holography. The camera incorporates an interferometer having a linearly displaceable mirror that can be used for phase-shifting. Although the camera works well, the need for phase-shifting remains an issue that restricts the application. In particular, phase-shifting requires the object to be nearly stationary for multiple exposures, hence, the temporal resolution can be sacrificed and the camera may be inappropriate for high-speed imaging. Moreover, because the amount of phase-shifting varies according to the wavelength of the illumination source, a large number of exposures is required for full-color imaging.
Still more recently, the inventor replaced the linearly displaceable mirror with an off-axis mirror that enables the interferometer to introduce high-frequency fringes that encode the phase information in the interferogram. With this change, the holographic camera is capable of capturing a holographic image with a single exposure of a scene illuminated with incoherent light without the need for any moving parts. While this camera is an improvement of the phase-shifting camera, limitations still exist. For example, because the camera requires an interferometer, which includes a beam splitter and two mirrors, the camera requires a relatively large volume of space and therefore may be unsuitable for use in applications in which such space is limited. Furthermore, the camera requires a relatively large number of parts, which increases the cost and complexity of the camera. Moreover, it is difficult to construct an interferometer that operates well in certain regions of the electromagnetic spectrum, such as the x-ray spectrum.
From the above discussion, it can be appreciated that it would be desirable to have an alternative system and method for performing incoherent digital holography.